Waste heat recovery

The invention provides a waste heat recovery device in which the heat efficiency of a Rankine cycle is improved. A waste heat recovery device (1) having a Rankine cycle (30) for circulating a working fluid, and a cooling circuit for circulating cooling water for an engine (2), wherein the heat source of a heater (31) of the Rankine cycle(30) is waste heat from the engine (2), and a condenser (33) of the Rankine cycle (30)is a heat exchanger for exchanging heat between the working fluid and cooling water in a third cooling water circuit (6)for circulating cooling water through a radiator(9)and not through the engine (2).